CMOS (Complementary Metal Oxide Semiconductor) image sensor is a sensor produced using a CMOS manufacturing technology, which converts the light incident on each pixel of the sensor into electrons using photodiodes and then outputs voltage signals in proportion to the number of electrons, thereby making them images.
Dynamic range within which a conventional CMOS image sensor properly responds to the brightness of the light is about 60 dB. In other words, the image sensor normally responds to the light ranging from the sensible minimal brightness of the light to about 1000 times of it, thereby outputting signals. Even in the art, a number of methods to widen the dynamic range of the CMOS image sensor have been suggested.
For example, U.S. Pat. No. 7,443,427 discloses a pixel structure having logarithmic dynamic range for light, and U.S. Pat. Nos. 7,442,910 and 7,209,166 suggest methods for increasing dynamic range by changing capacitors being electron storages in pixel through switch operation.
Further, Korean Patent Nos. 0835894 and 0865111 and U.S. Pat. No. 7,489,352 disclose methods in which two small and large photodiodes are constructed and two signals are output from the photodiodes, the two signals different responsivity to the light each other.
There are reported methods for extending a dynamic range of sensor by operating a transfer gate or a reset transistor several times in the process of obtaining signals from a normal pixel having a four-transistor structure, and others.
Since merits coexist with demerits in such various methods, it is not easy to say which method is remarkably superior to the others.